In today's growing demand after more bandwidth and smaller transmission delays the next step in the evolution of 3G-wireless communication networks meeting this demand will be the HSPDA (High-speed Packet Data Access) technology. HSPDA is an enhancement of the existing 3G wireless networks based on WCDMA (Wideband Carrier Division Multiple Access) Release 5 which will increase the peak downstream data rate from 384 Mb/s characteristical for WCDMA Release 99 networks to 14 Mb/s with reduced roundtrip time and retransmission delay, which on the user-side will provide for better end-user experience. On the side of operators the system capacity will be enhanced through the introduction of short TTI (Transmission Time Intervals), i.e. periods during which data is sent to the users in the wireless network and therefore better adaptated to rapidly changing transmission conditions on the radio link.
These improvements are mainly achieved by adaptive coding and modulation schemes and the transfer of the resource scheduling functionality from an RNC (Radio Network Controller) to Node B base station transceivers.
Using the adaptivity of the coding and modulation schemes employed, data transmitted from the base station to the different users may be coded and modulated in order to provide the optimum data rate possible for the individual users based on the channel quality.
Moving the scheduling functionality from the RNC to Node B base stations and thus closer to the air interface will reduce the delay time for retransmissions from typically about 100 ms in existing 3G wireless networks to about 10 ms, which is a dramatic improvement!
The HSPDA interface will also include a new high speed downlink data channel called HS-DSCH (High-Speed Downlink Shared Channel) which may be shared in the time domain by the users of the wireless network and a HS-DCCH (High-Speed Downlink Control Channel) where the control information necessary for decoding the data in the HS-DSCH for each user is stored.
The HS-DSCH is divided into 2 ms long groups of time slots called TTI (Transmission Time Intervals) during which data to the users of the wireless network is transmitted from the base station. The reduction of the TTI compared to the earlier WCDMA Release 99 will reduce the roundtrip delay between a mobile station (UE) and a base station (Node B) and achieve greater efficiency for the adaptive modulation and coding scheme, since they can be adapted more rapidly to the changing transmission conditions on the radio link.
HSPDA networks will, however, remain backward compatible with 3G wireless networks according to the WCDMA Release 99 specification.
One other important feature of HSPDA based networks will be Hybrid ARQ (Automatic Repetition reQuest) or HARQ for short. HARQ is a way of combining error detection information and error-correction codes together with ARQ when a transmission has failed. In chase combining only the part of the data that has been incorrectly received will be requested to be resent by the mobile station.
When it comes to the power necessary for transmission in HSPDA systems, it is calculated according to the required channel quality and the latest reported channel quality, i.e. the channel quality reported by a UE to a Node B during a previous data transmission.
However, in such a scenario, it is not taken into account whether the actual transmission is a completely new transmission or only a retransmission of previously erroneously received data.
Thus normally, the erroneously received data will be retransmitted by the base station to the UE after a certain amount of time based on the channel quality (CQI—Channel Quality Indicator) reported by the UE immediately before the start of the retransmission.
This situation is schematically illustrated in FIG. 1.
Thus the power of the retransmitted data will usually be unnecessarily high and therefore waste resources.
The present invention aims at obviating at least partially the retransmitted power problem mentioned earlier.